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Immersion method: The material is immersed in liquid nitrogen, liquid Freon, low temperature brine and other media for rapid freezing. This method freezes fastest.
Air-cooling method: The material is blown at low temperature and cold air to freeze the material to a certain temperature within a specified time.
Direct cooling method: The refrigerant or refrigerant is placed in the evaporative pipe to absorb the heat of the material for cooling purposes.
Vacuum refrigeration method: The use of vacuum to evaporate the moisture in the material to take away heat, cooling the material to achieve cooling purposes.
Regardless of the method used, materials should be guaranteed to freeze to a certain temperature within the specified time without substantial deformation.
In order to ensure that the ice in the material is insolubilized and vaporized (sublimation) and the vapors are continuously removed to ensure the normal sublimation, the degree of vacuum in the chamber must be lower than the saturated vapor pressure of ice at a certain temperature (below 610 pa).
The use of a cold trap is to trap water vapor and reduce the load of the vacuum pump. A properly designed cold trap will not cause the vacuum pump to fail, and the energy consumption is also low, but the design requirements for the refrigeration system and the cold trap are strict.
As ice continues to sublimate, the removal of vapors also removes the heat from the material, causing the material temperature (ice temperature) to continue to decrease, leading to a decrease in the saturated vapor pressure of the steam ice and a slower rate of sublimation. In order to maintain a certain rate of sublimation, it is necessary to constantly add heat to the material. Too little calorie supplement will reduce the rate of sublimation. Too much caloric supplement will cause the ice to melt, causing the material to collapse and freeze-dry.
Because the lyophilization process of the lyophilizer is complicated and the scope of working conditions is narrow, the quality of the lyophilized product will be reduced due to slight carelessness. Therefore, an automatic control system is required. The design of the lyophilization machine automatic control system requires simple operation, starting from the material into the button, quick-freeze vacuum sublimation drying one after the other, suggesting that the lyophilization is completed after the shutdown discharge. The relevant temperature and pressure control points should be carefully selected and reasonably controlled, and the associations of quick freezing, vacuum maintenance, and heating should be properly controlled, and the technological curves should be set for different materials.
The rapid popularity of freeze dryers cannot be separated from the eager demand of the industry for freeze dryers. In the industry, lyophilizers are already an indispensable industrial machine. In food and pharmaceutical companies, lyophilizers cannot be replaced. Here we will introduce in detail the types of lyophilizers.
August 24, 2024